1. Field of the Invention
The present invention relates to door locks and, more particularly, to a safety door lock that can be unlocked by a person inside the house with the fingers and that is not openable by any person outside the house.
2. Description of the Related Art
Various door locking devices have been disclosed for use to lock the door, and have appeared on the market. In order to let the door be slightly opened without allowing people outside the house to pass to the inside of the house, a door bolt may be used. A conventional door bolt is known comprised of doorplate and a jamb plate. The doorplate is fixedly fastened to the free end of the door panel, having an elongated sliding slot. The jamb plate is fixedly fastened to the doorjamb, having a chain and a slide bolt at the end of the chain for coupling to the sliding slot of the doorplate. There is known another design of door bolt in which the jamb plate has a hinged retainer bar; the doorplate has a hook. When the door closed, the hinged retainer bar is turned toward the hook of the doorplate, enabling the longitudinal sliding slot of the hinged retainer bar to be coupled to the hook of the doorplate.
The aforesaid prior art door bolts are still not satisfactory in function. If the door is slightly opened without allowing people outside the house to pass to the inside of the house, a person outside the door can use a cutting device to cut off the chain or the hook. Further, the aforesaid prior art door bolts are not detachable when installed. A person cannot install a conventional door bolt in the door of the room when put up at a hotel.
The present invention has been accomplished under the circumstances in view. It is the main object of the present invention to provide a safety door lock, which is not openable by a person outside the house when locked. It is another object of the present invention to provide a safety door lock, which can easily be opened by a person inside the house.
To achieve these and other objects of the present invention, the safety door lock is comprised of a positioning plate for fastening to a doorjamb, and a stop plate assembly for fastening to the positioning plate to stop a door panel in a closed status closing on the doorjamb in which the positioning plate is installed. The stop plate assembly comprises a plurality of back mounting lugs disposed near one end thereof for plugging in a mounting hole in a doorjamb to secure the positioning plate to the doorjamb, a longitudinal sliding way defined in a front side thereof, and serrated means longitudinally extended along one side of the longitudinal sliding way. The stop plate assembly comprises a bottom plate insertable into the longitudinal sliding way of the positioning plate, the bottom plate comprising a vertical rear extension portion extended from a rear end thereof at right angles for stopping the door panel in the closed position, a shell covered on the bottom plate, the shell having a bottom pivot pin and a through hole, a movable engagement plate mounted inside the shell, the movable engagement plate comprising a pivot hole disposed in a rear end thereof and coupled to the bottom pivot pin of the shell, a cam hole disposed in a front end thereof, and a tooth protruded from one side thereof and adapted to engage the serrated means of the positioning plate and to further stop the stop plate assembly in the positioning plate, a first spring member connected between the movable engagement plate and a part inside the shell and adapted to force the tooth of the movable engagement plate into engagement with the serrated means of the positioning plate, a button mounted inside the shell and partially extended out of the through hole of the shell for pressing by the user, the button having a bottom rod inserted into the cam hole of the movable engagement plate and adapted to bias the movable engagement plate and to further disengage the tooth of the movable engagement plate from the serrated means of the positioning plate when the button pressed by the user, and a second spring member connected between one side wall of the button and a-part inside the shell.